This invention relates generally to electrical load controllers for saving energy in commercial buildings, and in particular to a remotely accessible power controller for automatically disconnecting building lighting loads to comply with energy consumption codes applicable to the automatic shutoff of electrical lighting, and for automatically disconnecting or dimming building lighting loads to limit total connected power consumption below an agreed level in accordance with load curtailment agreements with public or private utility companies.
In an effort to make more efficient use of available energy resources, government authorities are adopting and mandating building energy codes. In particular, many jurisdictions have adopted the International Energy Conservation Code (IECC) which references ASHRAE/IESNA Standard 90.1 for commercial buildings. Part III (3) of that standard, concerning interior lighting, requires that all commercial buildings more than 5000 square feet in size must be equipped with automatic lighting shutoff in all spaces, by using time of day controls, occupancy sensor controls or other automatic controls that do not require operator intervention, so that energy can be saved during hours when the spaces are not occupied.
Modern building control systems generally allow an operator to control various operating systems from a centralized or remote building control station. For example, the building operator can monitor and exercise control over lighting systems, HVAC (heating, ventilation and air conditioning), water and waste disposal, furnaces, cooling towers, heat exchangers, ventilation dampers, fire detection and alarm systems, security cameras and other building service equipment. Such controls are implemented to maintain a customized set of building services to satisfy the comfort, safety and business needs of building tenants according to leasehold agreements.
The majority of existing commercial buildings are not equipped for automatic light shut off operation, and thus are not presently in compliance with ASHRAE/IESNA Standard 90.1. The retrofit modification of existing building lighting control systems with additional control wiring incurs considerable costs and provides only limited flexibility in configuring an existing lighting control network to accommodate automatic time-of-day disconnect schedules.
Moreover, some building operators may contract for lower rates from a utility company in exchange for voluntarily reducing its overall energy consumption or shedding selected electrical loads at the utility's request. Typically, such curtailment requests are made during peak demand periods (e.g., on a hot summer afternoon), and the building operator would be obligated to shed electrical loads by dimming or turning off lights, adjusting air conditioning thermostats, and terminating the operation of non-essential electrical machinery. In exchange, the utility company will charge the building operator lower overall rates for its energy consumption. Usually, such load shedding is accomplished by hand, turning off lights and non-essential loads room-by-room.
Many lighting installations are not equipped for dimming, so that a curtailment request when implemented means that the work force must be sent home. Consequently, there is a continuing interest in providing load-shedding control with dimming capability in existing lighting installations so that business can continue with reduced illumination while accommodating load-shedding curtailment requests, as well as accommodating automatic time-of-day load disconnect schedules when the work force is not present.
The majority of existing commercial buildings are not equipped for automatic light shutoff or dimming operation, so that considerable retrofit wiring is required. Conventional lighting control systems installed in existing commercial buildings control multiple lighting circuits that may be widely separated from each other by a substantial distance, for example in an office building, a manufacturing facility, in a restaurant, a large meeting hall or in a theater. In those installations that include dimming capability, each light or group of lights may be selectively controlled through a power dimmer, which is in turn connected to an individual controller or operator switch. In such a system, separate sets of wires run from a central controller to each light or group of lights. Sometimes, dimmers are included along with wall-mounted toggle switches for controlling the level of power supplied to each of the lighting circuits. Such dimmers usually take the form of rheostats that are manually set to the desired level of brightness. Consequently, even for small installations, a large amount of wiring is necessary to connect all of the lights with their respective power dimmers, and to connect the power dimmers to their respective controllers.
In commercial building lighting installations, two-phase or three-phase power is supplied, with phase A power being applied to one group of electrical loads, phase B power being applied to another load group and phase C power being applied to another load group. Consequently, in a large area lighting installation, some of the lighting loads will be supplied by phase A power, other lighting loads will be supplied by phase B power and other lighting loads will be supplied by phase C power. Dimming circuits typically utilize semiconductor switching devices whose duty cycle is controlled with reference to the phase of the current waveform. Because of the phase difference, it is difficult to utilize conventional light dimming systems that employ a microprocessor controlled memory unit for selectively controlling the application of power to a specific group of lighting loads, individual ones of which may be separately energized by phase A, phase B power and phase C power.
Consequently, a lighting controller for performing automatic turn off and dimming operations is needed in which the amount of retrofit wiring required for connecting the controller to multiple power dimmers and lighting loads is substantially reduced. Such a lighting control and dimming system desirably should be operable via power line carrier (PLC) signaling over existing AC power conductors by which the ON-OFF and dimming operation of groups of individually-dimming and non-dimming lighting loads can be controlled, without appreciably increasing the amount of wiring. Moreover, in large area lighting, multiple power phase installations, the lighting control and dimming system should be capable of reliable operation in which power disconnect signals and dimming signals from a remote controller or a master controller can be communicated independently of line phase.
Power disconnect and dimming signaling for controlling the AC power applied to lighting loads has been implemented by conventional power line carrier (PLC) communication systems using the existing alternating current (AC) power lines for conducting control signals to addressable electronic control devices, for both dimming and non-dimming lighting loads connected to the power lines. In general, an addressable PLC pulse receiver is connected between the power line and each load that is to be controlled, and at least one PLC encoded command signal pulse transmitter is connected to the power line. By utilizing the existing power conductors as the means for communication between the PLC transmitter and receivers, such control systems can be installed without requiring the installation of additional wiring. Further, utilization of the power conductors also provides a greater physical range of control than could be achieved via infrared, ultrasonic or FM control signaling systems.
Typically, the PLC control signals are communicated at a substantially higher carrier modulation frequency (i.e., frequencies at least two orders of magnitude higher than the power line frequencies), e.g., at 120 kHz to 200 kHz or higher as compared to conventional alternating current power distribution frequencies (e.g. 50/60 Hz or 200/400 Hz). There are substantial high frequency noise and interfering signals such as harmonics of the power signal, switching transients, etc. that interfere with the PLC command signals. Numerous techniques are known for operating in a noisy environment for example, in some cases, the signaling commands are repeated to assure transmission, spread spectrum signals are used in other cases, in addition to many other techniques.
A major limitation on the use of power line carrier communications is spurious signals and background noise including impulse noise. Such noise can originate from the power source, the distribution network, loads coupled to the distribution network and from remote sources. For example, the alternating current power delivered from a public utility is not a pure sine wave. The AC supply current contains harmonics that can interfere with PLC command signals. Additionally noise may be introduced from the loads (including switching transients). By way of illustration, if the load is an active device such as a dimmer and lamp, the dimmer may “chop” the 60 Hz AC power waveform to reduce the lighting intensity. This introduces harmonics and high frequency noise on the power distribution conductors.
This high frequency noise makes it more difficult to communicate reliably over power lines particularly since some of the harmonics and noise associated with the power distribution fall within the frequency range of the PLC command signals. Such noise is not constant with respect to time, it also varies from place to place in the power distribution network. Moreover, a conventional AC power line network is used for power distribution to several electrical load devices. Each of a variety of load devices can conduct a significant level of noise back onto the power line. Different loads and control devices produce different types and degrees of noise that may interfere with the flow of information over the power line.
Another potential limitation on PLC signaling is signal attenuation. Due in part to the diverse impedance levels of the electric loads coupled to a PLC network, digital pulse communication signals may undergo more than 40 dB of attenuation before being captured by a receiver. This significant attenuation in combination with noise interference makes reliable PLC communication very difficult.
The noise and attenuation problems existing in a particular power line network may vary substantially from one network to another depending on the types of devices connected to or coupled in some way to the power line network. Moreover, even the mode of operation of particular load devices on the power line network may differentially affect the noise or attenuation levels throughout the network. For these reasons, a signaling protocol is preferred for efficiently and accurately transmitting information from a source node to a receiving node on a power line network.
One conventional signaling protocol, “X-10,” provides sensing, control and communications over AC power lines. The X-10 system was developed by Pico Electronics of Fife, Scotland and X-10 compatible products are distributed in the United States by X-10 (USA) Inc. of Northvale, N.J. The X-10 system utilizes a signaling means whereby simple control signals (i.e., on, off, dim, brighten, etc.) are transmitted over pre-existing power conductors for remotely controlling power to lighting and other electrical loads. The X-10 power line data communication protocol is disclosed in U.S. Pat. Nos. 4,200,862; 4,628,440; and 4,638,299.
Another protocol for two-way communications links is the Electronic Industries Association Consumer Electronics Bus (CEBus) protocol for radio frequency media, power line carrier, infrared media and twisted pair media. The CEBus protocol provides operating standards for establishing a local area network, or LAN, over five physical distribution media: electrical power conductors (PLBus), twisted pair (TPBus), coaxial cable (CXBus), infrared light (IRBus) and low power wireless radio (RFBus). This standard specifies how devices are to send and receive information, the media available to them for communication purposes and the format for the information the devices communicate to each other. In particular, the CEBus standard permits devices made by various manufacturers to be able to communicate with each other.
In the X-10 system and as well as the CEBus and other encoded protocol systems, for example LonWorks, BACnet and Echelon, the carrier detection threshold level is fixed. In selecting a threshold level for such a system, the level must be relatively high to provide some immunity from expected noise. The reliability of such systems is compromised when the signal-to-noise ratio is low. In particular, this increases system vulnerability to spurious signals and sensitivity to electrical noise, causing lost messages, false interpretation and spurious activation. Different types of electrical noise that can interfere with PLC encoded protocol systems are developed on the AC power line from electrical equipment such as power tools and machines that use induction motors, electronic and magnetic ballasts, personal computers, and pumps. The noise may have even originated from a nearby building that is supplied from the same power distribution transformer. These types of noise disturbances can occur any time during the day, night or on a weekly basis, causing erratic communication including false turn-ON/turn-OFF of PLC—controlled devices.
It is essential that the PLC signal strength be strong over the entire network. Low signal strength means erratic or loss of control on the most distant devices from a PLC transmitting device. Signal strength loss on a circuit can be due to several factors, including the number of interconnected PLC devices, power conductor losses and non-PLC devices on the circuit.
Typically, each control device on the PLC network can reduce the signal strength progressively by as much as 15%-20% per device. For example, if a PLC device transmits a 4V signal strength on its power line then the next (2nd) nearest device on the same power line will load the signal strength down by 20% to 3.2V. The third device would reduce the remaining signal again by 20% to 2.6V, the fourth to 2.08V, the fifth to 1.664V, the sixth to 1.33V, the 7th to 1.065V, the 8th to 0.852V, the 9th to 0.68V, and the 10th device to 0.545V.
Power wiring losses must also be taken into account. Wiring loss is due to the power wiring resistance and capacitance losses that reduce signal strength. The greater the distance between a PLC device to another PLC device the more loss of signal strength occurs. The wiring has very little effect on signal strength if the PLC devices are in the same multi-ganged wall box or wiring distance is very short. However, for each 50 feet length of 12 AWG Romex from one PLC device to another a loss of about 18% of the signal strength should be expected.
For example, if a 150 ft. length of 12 AWG Romex is connected between two PLC devices and one device sends a 4.0 V signal strength command to the other unit, a signal strength of 1.77 V would be expected after losses: after the first 50 ft. of wire length, the signal strength would drop by 18% to 3.28 V, the next 50 ft. (100 ft. total) distance the signal strength would drop another 18% to 2.69 V, the last 50 ft. (150 ft. total) of distance signal strength would drop another 18% to 2.21 V. When the PLC receiving device loss of 20% included, the signal strength remaining would only be 1.12 V.
Other PLC devices or non-PLC devices on the PLC network that can degrade the signal strength include: passive PLC couplers (used to connect phases together), and non-PLC devices such as personal computers, laser printers and power surge suppressors. When the losses are calculated and the other factors mentioned are added in then it is easy to understand why the PLC signals may be too weak to activate a receiver. Some suppliers of PLC devices require a minimum of 50-100 mV signal strength for reliable data capture operation. Preferably, a minimum of 500 mV of signal strength should be available at any signal receiving node on the network.
Many vendors recommend using a passive coupler to couple PLC signals between phases. These couplers will further reduce the signal strength. Sometimes a repeater amplifier will be used to jump phases and amplify the signal strength. These do not solve the problem of other circuits that are on the same phase that might need to be amplified.
In a network system the PLC signal must cross phases if some PLC devices are on one phase and some PLC devices are on the other. If a passive filter (non-amplifying device) is used, a loss of about 20% of the signal strength can be expected on the other phase. These signal bridges are normally hardwired at the distribution panel. Since the distribution panel will normally be several feet from the PLC devices the wiring loses will further reduce the PLC signal strength. These loses usually cause a critical reduction of signal strength on the other phases to allow reliable communication across the PLC network.